Ophthalmic lenses for eyeglasses may be manufactured from many different materials, such as glass, plastic, polycarbonate, and thermoplastic resins. An ophthalmic lens undergoes a series of molding and/or surfacing/buffing operations that determine the geometry of both the convex and concave optical surfaces of the lens. The surfacing may be followed by appropriate surface treatments, such as multicoat, hardcoat or coloring. The final step in ophthalmic lens manufacture is edging, which consists of machining the lens edge or periphery to conform the lens' dimension and shape to the dimension and shape of the frame in which the lens is to be mounted.
The edging step is typically carried out on a grinding machine comprising an abrasive wheel, such as a diamond abrasive wheel, that is used to remove lens material. Before the edging step, a mounting element is fixed on the center of the convex surface of the ophthalmic lens to form an assembly that can be mounted in the edger. During the edging step, the lens is held by two clamping elements of the grinding machine. The relative movement of the ophthalmic lens and the abrasive wheel is controlled, generally digitally, so as to obtain the required size and shape for the ophthalmic lens.